1. Field of the Invention
The present invention relates to a bonding member, a bonding method, and a method for manufacturing an image display apparatus.
2. Description of the Related Art
An image display apparatus that has a large number of electron-emitting devices aligned thereon and is arranged so as to oppose to a fluorescent plane has been developed as a light and thin flat-type display apparatus. Such a flat-type image display apparatus (flat panel display) needs to maintain a degree of vacuum in the inner part of an envelope thereof, for instance, at 10−5 to 10−6 Pa.
A conventional method for achieving such a degree of vacuum involves releasing a gas adsorbed on the surface in the inner part of the envelope in an evacuating step through a baking treatment process of heating the envelope. However, it has been difficult to sufficiently release the adsorbed gas on the surface using such a method, so that there was a case in which a high degree of the vacuum could be hardly obtained.
Conceivably, the degree of the vacuum in the inner part of the envelope may be increased by the following method. This method includes the steps of: charging a back substrate, a side wall and a front substrate into a vacuum apparatus; baking them and irradiating them with an electron beam in a vacuum atmosphere to release the adsorbed gas on the surface; subsequently forming a getter film; and directly bonding the side wall with the back substrate and the front substrate through a bonding member in a vacuum atmosphere to seal them to form an envelope.
A bonding member, which can be used in a process of forming such a hermetically sealed envelope, is required to have the following characteristics:
1. Heat resistance: heat resistance in a baking step in a vacuum (forming a high vacuum)
2. Air tightness: capable of keeping a high vacuum (minimal vacuum leak and minimal gas permeation) but only in a part necessary to be kept vacuum,
3. Adhesiveness: adhesiveness to glass member
4. Gas-releasing property: low gas-releasing property (keeping high vacuum)
A usable bonding member having such characteristics includes a glass frit and a metal. This method can sufficiently release the adsorbed gas on the surface with an electron beam cleaning technique and can show a sufficient effect of gas absorption without oxidizing the getter film. The method also does not require the use of an exhaust pipe. Accordingly, it does not waste space in the image display apparatus.
However, when the image display apparatus is sealed in vacuum by using the glass frit, the glass frit needs to be heated at a high temperature of 350° C. or more at least once. At this time, a large amount of air bubbles generate from the glass frit, which causes a problem of decreasing the air tightness and the sealing strength of the vacuum envelope and decreases the reliability.
For this reason, a method is proposed, which is directed at achieving hermetically sealed bonding by using a glass frit and a metal as a bonding member.
Japanese Patent Application Laid-Open No. 2002-184328 discloses a metallic sealing material, which has a bent portion or a curved portion and has a bonding function.
In addition, National Publication of International Patent Application No. 2002-515392 discloses a method of forming one end of a glass frit bar into a male bonding portion, forming one end of another glass frit bar into a female bonding portion, and connecting the male bonding portion with the female bonding portion, as a method for increasing the air tightness.
Furthermore, a high accuracy lamination method is also proposed, which does not relate to air bubbles generated by heating, but includes removing air bubbles that enter into the space when affixing the adhesive sheet to the plate. Japanese Patent Application Laid-Open No. 2001-279195 discloses a method of making air bubbles that enter into the space in a laminating step escape via a through hole or a groove, which has been formed in the adhesive sheet.